High-frequency propagating modes in vitreous silica at 295 K

Collective modes in vitreous silica (v-${\mathrm{SiO}}_2$) are found at 295 K and at momentum transfers Q=1.5 and 2.0 ${\mathrm{nm}}^{\mathrm{-}1}$. They propagate with a sound velocity of ≈ 6000 m/s, a value equivalent to that in the Q→0 limit, and to that recently measured at 1050 K in the 1–3.5 ${\mathrm{nm}}^{\mathrm{-}1}$ Q range. The data complete the scenario on the acousticlike dynamics in v-${\mathrm{SiO}}_2$, showing its temperature independence and propagating rather than localized nature in the whole 295–1050 K and 0.01–2.0 ${\mathrm{nm}}^{\mathrm{-}1}$ temperature and Q ranges.